There's a very particular moment that many of us have already experienced: you dial a number and nothing happens. No ringing, no voicemail, just silence. Then you glance at the signal bar at the top of the screen, and you realise the problem isn't with your phone.
A major carrier outage, a storm bringing down power lines, a fire, a flood, or simply a stadium or a beach where 40,000 people are all trying to make a call at once: in every one of these cases, the mobile network doesn't shut down all at once. It degrades, layer by layer. And within that degradation there's a fairly consistent order of survival: voice usually fails first, data next, and SMS holds out longer than anything else.
Understanding why gives you the means to stay reachable when everyone around you no longer is.
Why texts still get through when calls don't
The answer lies in a technical quirk inherited from the 1990s, and never contradicted since.
A tiny message travelling through the gaps
Originally, SMS wasn't designed as a commercial service at all, but as a repurposed use of the GSM network's signalling channel. That channel is the service lane the network constantly uses to talk to handsets: to know where they are, to authenticate them, to announce an incoming call. It's narrow, but it has priority and it keeps working even when the "useful" communication channels are full.
A 160-character SMS weighs 140 bytes. That's negligible on the scale of modern networks. Where a voice conversation requires a channel held open continuously for several minutes, and video eats up megabytes per second, an SMS only needs a fraction of a second of availability to slip into the traffic.
"Store and forward": patience as a feature
The second decisive advantage: SMS doesn't require sender and recipient to be reachable at the same instant. The message goes to an intermediate server run by the carrier — the SMSC (Short Message Service Center) — which stores it, then tries to deliver it, and tries again, and again, for hours or even several days depending on the carrier's settings.
That's the exact opposite of a phone call, which is an all-or-nothing communication: either the circuit is established right now, or it fails.
In a crisis, that difference changes everything: a failed call is lost, whereas a sent text generally arrives in the end, even twenty minutes late.
It also explains a phenomenon often observed after a major event: messages arrive in a burst, all at once, as soon as the network clears.
What about RCS?
RCS, which is gradually replacing SMS on Android as well as iPhone, is an IP service. It needs a working data or Wi-Fi connection. In practice, that means that if the cell network is congested or the fibre feeding the tower is cut, your RCS conversation stops dead.
The good news: modern messaging apps automatically fall back to SMS when RCS fails. You just need to make sure that fallback hasn't been disabled in the settings — more on that below.
What actually fails during an outage: three scenarios
Not all outages are alike, and the right reflexes differ.
Scenario 1: congestion
A concert, a Bastille Day fireworks display, the back-to-school rush in a packed railway station, or a crowd of onlookers at the scene of an accident. The network is working perfectly, but it doesn't have enough radio resources for everyone.
What still works: SMS, with delays. Sometimes emergency calls, which get network priority.
The right reflex: don't keep redialling. Every call attempt consumes signalling capacity and makes congestion worse for everyone. One clear text is worth more than ten aborted calls.
Scenario 2: a carrier outage
A configuration error, a software incident in the core network, a cable severed by a digger. This type of incident is rare but spectacular, and can leave millions of subscribers without service for several hours.
What still works: in France, regulations require that emergency calls be routed via any available network. If your carrier is down but a competitor's tower covers your location, your phone can switch over to reach 112. Your ordinary text messages, on the other hand, do depend on your own carrier.
The right reflex: turn on Wi-Fi calling and Wi-Fi texting if you have a working router on a different infrastructure.
Scenario 3: a power cut
This is the most underestimated scenario. A cell tower consumes electricity. Most sites have backup batteries, but their autonomy is limited — often in the range of a few dozen minutes to a few hours depending on the equipment. Strategic sites are backed up by generators; the others gradually go dark.
After storms like those that have hit western France in recent years, the post-event reports published by carriers and relayed by the Arcep show that towers come back online in step with the electricity grid, several hours behind.
What still works: your phone, as long as it has battery, plus a still-powered tower within range. A high-capacity power bank kept charged in a drawer makes a considerable difference here: without mains power, the smartphone becomes the weak link well before the network does.
FR-Alert: the text that finds you without knowing your number
Since 2022, France has been rolling out FR-Alert, the national public warning system. It relies on a technology many people confuse with SMS, but which is fundamentally different: cell broadcast.
How it works
Rather than sending a message to a list of numbers, the cell tower broadcasts the alert to every phone within its coverage area, like a radio station. The consequences:
| Standard SMS | FR-Alert (cell broadcast) | |
|---|---|---|
| Recipient | One specific number | Every handset in an area |
| Number known to authorities | Required | No |
| Sensitive to congestion | Yes | Very little |
| Prior registration | — | None |
| Works while roaming | Depends on the carrier | Yes, including foreign tourists |
The major advantage: the system requires no collection of phone numbers. That's an important point for privacy, one regularly stressed by the CNIL whenever warning systems come up: no population database is created here.
The Ministry of the Interior, which runs the system, has supplemented FR-Alert with a conventional SMS channel for certain areas poorly covered by cell broadcast.
What you should check on your phone
Government alerts are enabled by default, but they may have been switched off by mistake.
- On iPhone: Settings → Notifications, right at the bottom of the screen, the "Government Alerts" section.
- On Android: Settings → Notifications → Wireless emergency alerts (the wording varies by manufacturer).
Leave them switched on. The alert tone is deliberately piercing and overrides silent mode: it's unpleasant, and that's the point.
Getting your phone ready: a realistic checklist
This isn't about survivalism, just digital common sense. Here's what genuinely makes a difference.
1. Save battery before you need it
A phone desperately searching for a network that isn't there burns through an enormous amount of energy: it transmits at full power continuously. If you know the network is down and you're not expecting an imminent call, Airplane mode is your best ally. Come out of it every thirty minutes to let queued messages download, then switch it back on.
Keeping a 20,000 mAh power bank charged to 80% in a bag or a hallway drawer will see you through several days of frugal use. In areas regularly hit by power cuts, a portable solar charger is a credible complement, provided you don't overestimate its real output.
2. Don't depend on digital alone
Your emergency contacts live in your phone. If it dies, they vanish with it. Writing five essential numbers on a slip of paper tucked into your wallet remains, in 2026, one of the most effective measures there is. A pocket address book does the job perfectly.
In the same spirit, a battery-powered or hand-crank portable radio remains the only reliable way to receive official information when neither the mobile network nor the internet is working: France Inter and France Bleu carry public-service information duties in crisis situations.
3. Check your messaging settings
Three things to check today, while everything is calm:
- Automatic SMS fallback: in your messaging app, make sure that sending as SMS when RCS or iMessage fails is allowed. On iPhone this is the "Send as SMS" option; on Google Messages, the automatic fallback on failure.
- Wi-Fi calling (VoWiFi): when enabled, it lets you keep calling and texting through an internet router, even with no mobile coverage.
- Your SIM card PIN: if you have to restart your phone and you've forgotten the code, you lose network access. It's a classic.
4. Send the right messages
In degraded conditions, the quality of the message matters as much as its transmission.
- Be brief. A single 160-character segment stands a better chance of getting through than a long message split into five parts, since each segment has to be delivered separately.
- Avoid emojis and unusual accented characters if you want to stay within the standard GSM alphabet: a single special character switches the message to Unicode encoding and cuts capacity to 70 characters.
- Lead with the essentials: who you are, where you are, whether you're OK, whether you need help. No "call me back", which assumes voice is working.
- One group message rather than ten individual ones: less traffic, less waiting.
The numbers and services that matter
A few reference points worth knowing, all free and reachable from any mobile:
- 112: the European emergency number, reachable even without a valid SIM card and via any available network.
- 114: the emergency number by text message, intended for deaf and hard-of-hearing people — but usable by anyone when speaking is impossible. It works when voice doesn't.
- 196: sea rescue.
- 191: aeronautical rescue.
114 deserves particular attention in the context we're discussing here: it is officially the only French emergency number reachable by text message. It isn't designed as a convenience alternative, but it exists precisely for situations where a voice call is impossible.
The aftermath: when the scams arrive
One last point, far too rarely mentioned. After every major event — storm, flood, nationwide outage — a wave of fraudulent messages invariably follows in the days that come.
The patterns are always the same:
- fake "compensation" texts supposedly sent by your insurer or your carrier;
- bogus appeals for donations to help victims;
- messages announcing a "goodwill gesture" with a refund link asking for your bank details.
The rule never changes: no legitimate organisation asks for bank details by text message. When in doubt, the public service Cybermalveillance.gouv.fr and the 33700 platform, dedicated to reporting unwanted text messages, are the right places to turn. Just forward the suspicious message to 33700, free of charge.
In summary
SMS is an old technology, limited, without end-to-end encryption by default, and often mocked next to modern messaging apps. But it's precisely that rustic simplicity that makes it a safety net: tiny, patient, able to squeeze through where nothing else can.
The key takeaways:
- During an outage or congestion, write, don't call.
- A short message with no emojis has a better chance of arriving.
- Check right now that government alerts and automatic SMS fallback are enabled.
- Battery is the real weak point: plan ahead for it.
- 114 lets you reach emergency services by text when voice isn't possible.
- After the crisis, be wary of "compensation" messages.
The best preparation costs almost nothing: five minutes of settings today, and a little discipline in how you write your messages on the day everyone around you is frantically hitting "call back".
